We propose is to examine molecular mechanisms of HIV-mediated inflammation in the presence of antiretroviral therapy (ART) and drugs of abuse. Substance abuse often exacerbates neuroinlammation. We will use methamphetamine (meth) as it has been shown to enhance HIV CNS disease, and dopamine as a model for drug abuse as all substances of abuse increase CNS extracellular dopamine. HIV infection of the CNS results in chronic inflammation that leads to cognitive deficits in more than 50% of infected people. This inflammation and subsequent CNS damage is not mitigated with ART. Thus, triggering inflammation is a key process in HIV disease and therapies to limit immune activation and neuroinflammation must be developed to improve the quality of life of HIV infected people. HIV enters the CNS soon after peripheral infection and despite ART, persists within infected cells. HIV entry into the brain is mediated, at least in part, by infected monocyte transmigration across the blood brain barrier (BBB). A mature subset of monocytes that expresses CD14 and CD16 is a key mediator of HIV CNS disease and is increased in number in the peripheral blood of HIV infected people. These monocytes are productively infected with HIV and are primed to cross the BBB. Within the CNS, HIV infected monocytes may differentiate into macrophages that can persist for years. This leads to infection/activation of CNS cells, resulting in chronic neuroinflammation with the production of virus and/or viral proteins, cytokines and chemokines. Chemokines, in particular CCL2, increase transmigration of peripheral blood monocytes, continuing neuroinflammation. Thus, chronic inflammation is thought to mediate neuronal damage in a large percentage of infected individuals by mechanisms not well understood. We will characterize the effects of meth, HIV and tat, and ART on monocyte entry into the CNS and on subsequent neuroinflammation. We will test potential therapeutics to limit inflammation and guide efficacy of ART. We hypothesize that meth use combines with HIV infection to exacerbate neuroinflammation and compromise BBB integrity, increasing transmigration of uninfected and HIV-infected monocytes into the brain, leading to cognitive impairment. Based on our new preliminary data that tenofovir increases junctional proteins on the BBB, we also hypothesize that certain ART regimens, especially in meth abusers, may negatively impact cognitive function by synergizing with meth to increase BBB permeability and neuroinflammation. We will characterize effects of meth, HIV and tat, and ART on cytokines, chemokines, and adhesion molecules elaborated by and expressed on CD14+CD16+ monocytes that facilitate entry into the CNS, and in causing BBB permeability and transmigration of CD14+CD16+ monocytes resulting in inflammation, and the impact of ART. We will use a murine model to evaluate the in vivo impact of meth, HIV and its proteins, and ART on BBB permeability and migration of inflammatory cells into the brain. We will also examine effects of meth or dopamine, HIV tat, and ART on cytokine release from CNS cells that mediate inflammation.